FN MAG SLEEVE — FN 509M 9mm — 17-Round Magazine Sleeve, Black (20-100355 / 20100355 / UPC 845737010164)

Short meta description (SEO): FN MAG SLEEVE for the FN 509M — black polymer 17-round magazine sleeve (part #20-100355 / 20100355). Convert full-size 17-round FN magazines for comfortable, reliable use in FN 509 Midsize pistols. UPC 845737010164.

Product Overview

The FN MAG SLEEVE (20-100355 / 20100355) is a factory-fit polymer magazine sleeve engineered to adapt FN 17-round 9mm magazines for use with the FN 509 Midsize (509M) platform. Made from impact-resistant polymer, this OEM sleeve slides over a 17-round magazine to provide a secure, ergonomic grip surface, prevent over-insertion, and deliver a near-factory fit and finish on the midsize frame. It’s a small, inexpensive accessory that makes running full-size capacity mags in a midsize pistol both practical and comfortable. MidwayUSA+1

Key Features

• Fit / Model: FN 509M (Midsize) — designed specifically for 17-round 9mm magazines. GunMag Warehouse+1

• Manufacturer Part Numbers: 20-100355 (SKU) / 20100355. GrabAGun+1

• UPC: 845737010164. GrabAGun

• Material: Durable, impact-resistant polymer for lightweight strength and longevity. GunMag Warehouse

• Color: Black — low-profile, OEM appearance. OpticsPlanet

• Installation: Tool-free slide-on design for fast installation and removal. MidwayUSA

Why You Need This Sleeve

Using a full-size 17-round magazine in the FN 509 Midsize without a sleeve can leave the magazine over-inserting, produce an awkward grip, or create an inconsistent ride height. The FN MAG SLEEVE restores the intended grip geometry, adds a comfortable palm surface, and prevents excess magazine movement — all while preserving reliable feeding and magazine seating. It’s the go-to accessory for shooters who want the capacity of a full-size mag with the handling benefits of a midsize pistol. dfcarms.com+1

Performance & Practical Benefits

• Improved Ergonomics: Extends the grip surface in the correct location so the pistol handles naturally with a 17-round mag installed. GunMag Warehouse

• Factory Fit & Finish: OEM design ensures seamless integration with FN 509M frames and minimal snag for concealment or draw. Palmetto State Armory+1

• Durability: Robust polymer resists dings, scratches, and everyday carry abuse. GunMag Warehouse

• Cost-Effective: An inexpensive upgrade that solves common fitment and comfort issues when running larger magazines in midsize pistols. GrabAGun

Compatibility & Fitment Notes

• Specifically intended for the FN 509 Midsize (509M) pistols using the OEM 17-round 9mm magazine. It does not convert full-size frame geometry and may not be compatible with aftermarket magazines that differ in external dimensions. Always verify magazine model and fit before purchase. The Mag Shack+1

Installation & Use

1. Ensure the magazine is unloaded and the firearm is clear.

2. Slide the FN MAG SLEEVE over the 17-round magazine until it seats flush with the magazine body.

3. Insert the magazine into the 509M and confirm proper seating and retention.

4. Function-check (dry) to ensure reliable feed and release.
   The sleeve is tool-free and reversible — remove it for range use or re-install for everyday carry as desired. MidwayUSA+1

Care & Maintenance

Wipe clean with a damp cloth and mild soap if needed. Avoid harsh solvents for prolonged exposure. Inspect periodically for cracks or excessive wear — replace if any damage is found to maintain secure fit and reliable operation. GunMag Warehouse

Who Should Buy This

• FN 509M owners who want to run 17-round magazines without compromising grip ergonomics.

• Concealed carriers seeking a low-profile solution to retain full-size capacity in a midsize package.

• Range users and instructors who swap between full-size and midsize configurations and need consistent handling.

• Any shooter wanting an OEM, reliable, and affordable mag sleeve replacement. dfcarms.com

SEO Keywords (for search optimization)

FN MAG SLEEVE, FN 509M mag sleeve, FN 509M 17-round sleeve, 20-100355, 20100355, UPC 845737010164, FN 509 midsize magazine sleeve, 9mm 17rd sleeve, FN magazine adapter sleeve, OEM FN mag sleeve.

Final Thoughts

Small accessories make a big difference. The FN MAG SLEEVE (20-100355 / 20100355) offers a factory-fit, durable, and affordable way to use 17-round magazines in your FN 509M while restoring natural ergonomics and reliable function. If you want the capacity of a full-size magazine with the handling of a midsize pistol, this sleeve is an essential, no-fuss solution. MidwayUSA+1

The End